1. Field of the Invention
The invention relates to a plasma display panel, and more particularly to a phosphor layer as one of parts constituting a plasma display panel, in particular, a phosphor layer which emits a blue light.
2. Description of the Related Art
A plasma display panel (PDP) is recently popularized as a flat display because of its advantages that a plasma display panel is thin, a big screen can be readily fabricated with a plurality of plasma display panels, a plasma display panel has a broad viewing angle, and a plasma display panel has a high response speed.
FIG. 1 is a perspective view of a display cell in a conventional three-electrode surface-discharge AC type plasma display panel 300.
As illustrated in FIG. 1, the display cell includes a front substrate 351 and a rear substrate 352 arranged in parallel with each other. In use of the plasma display panel 300, the front substrate 351 is directed to a viewer.
The front substrate 351 is comprised of an electrically insulating substrate 302 composed of transparent material such as glass, a plurality of scanning electrodes 303 and common electrodes 304 (only one of them is illustrated in FIG. 1) formed on a surface of the electrically insulating substrate 302 facing the rear substrate 352, trace electrodes 305 formed on the scanning electrodes 303, trace electrodes 306 formed on the common electrodes 304, a dielectric layer 312 formed on the electrically insulating substrate 302, covering the scanning electrodes 303, the common electrodes 304 and the trace electrodes 305 and 306 therewith, and a protection layer 313 formed on the dielectric layer 312.
The scanning and common electrodes 303 and 304 are alternately arranged and spaced away from each other by a certain distance in parallel with each other.
The trace electrodes 305 and 306 reduce electrical resistances of the scanning and common electrodes 303 and 304.
The protection layer 313 protects the dielectric layer 312 from discharges, and is composed of magnesium oxide (MgO), for instance.
The rear substrate 352 is comprised of an electrically insulating substrate 301 composed of transparent material such as glass, a plurality of data electrodes 307 (only one of them is illustrated in FIG. 1) formed on a surface of the electrically insulating substrate 301 facing the front substrate 351 such that the data electrodes 307 extend perpendicularly to the scanning and common electrodes 303 and 304, a dielectric layer 314 formed on the electrically insulating substrate 301, covering the data electrodes 307 therewith, a partition walls 315 formed on the dielectric layer 314, and a phosphor layer 311 formed on both an exposed surface of the dielectric layer 314 and sidewalls of the partition wall 315.
In the display cell illustrated in FIG. 1, through the rear substrate 352 is designed to include the transparent substrate 301, it is not always necessary for the electrically insulating substrate 301 to be transparent.
The partition wall 315 defines a discharge gas space and a display cell (a pixel) 308.
When viewed perpendicularly to the electrically insulating substrate 301, the partition wall 315 is in the form of a grid. The partition wall 315 is comprised of vertical partition walls 315a extending in parallel with the data electrodes 307, and horizontal partition walls 315b extending perpendicularly to the vertical partition walls 315a. 
The vertical and horizontal partition walls 315a and 315b are equal in height to each other. A height of the vertical and horizontal partition walls 315a and 315b from a surface of the electrically insulating substrate 301, that is, a total thickness of the dielectric layer 314 and the partition wall 315 is 120 micrometers, for instance.
The display cell 308 is filled with a discharge gas composed of a mixture of helium, neon, xenon or other noble gases singly or in combination. The phosphor layer 311 receives ultra-violet rays resulted from discharge of the discharge gas, and resultingly, emits a visible light 310 towards a viewer.
FIGS. 2A to 2F illustrate steps to be carried out in a method of fabricating the plasma display panel 300. FIGS. 2A, 2C and 2E are plan views of the rear substrate 352, and FIGS. 2B, 2D and 2F are cross-sectional views taken along the lines 2B—2B, 2D—2D and 2F—2F in FIGS. 2A, 2C and 2E, respectively.
Hereinbelow is explained a method of fabricating the plasma display panel 300 with reference to FIGS. 2A to 2F.
As illustrated in FIG. 1, the scanning and common electrodes 303 and 304 are formed on the electrically insulating substrate 302 such that they are alternately arranged and extend in parallel with each other.
Then, the trace electrodes 305 and 306 are formed on the scanning and common electrodes 303 and 304, respectively.
Then, the dielectric layer 312 is deposited on the electrically insulating substrate 302 such that the scanning and common electrodes 303 and 304 and the trace electrodes 305 and 306 are fully covered with the dielectric layer 312.
Then, the protection layer composed of MgO is formed on the dielectric layer 312.
Thus, there is completed the front substrate 351.
With respect to the rear substrate 352, as illustrated in FIGS. 2A and 2B, a plurality of the data electrodes 307 are formed on the electrically insulating substrate 301 so that they extend in a common direction.
Then, as illustrated in FIGS. 2C and 2D, the dielectric layer 314 is formed on the electrically insulating substrate 301 so as to cover the data electrodes 307 therewith.
Then, as illustrated in FIGS. 2E and 2F, the partition wall 315 is formed on the dielectric layer 314.
The partition wall 315 may be formed by sand-blasting or printing. For instance, the partition wall 315 is formed by sand-blasting, as follows.
First, there is made partition-wall paste comprised of a mixture of filler, glass powder, binder and solution.
Then, the partition-wall paste is coated onto the dielectric layer 314. Then, solution contained in the partition-wall paste is evaporated. Thus, there is formed a paste layer (not illustrated).
Then, a dry film is adhesively put on the paste layer, and then, is patterned.
Then, the paste layer is sand-blasted with the thus patterned dry film being used as a mask. Thus, the paste layer is patterned in accordance with a pattern of the dry film.
Then, the dry film is removed, and the paste layer is baked.
Thus, binder contained in the paste layer is evaporated, and simultaneously, glass powder is melted and solidified again. As a result, there is formed the partition wall 315 composed of filler and glass.
The partition wall 315 is formed in the form of a grid such that the vertical and horizontal partition walls 315a and 315b are equal in height to each other.
Then, as illustrated in FIG. 1, the phosphor layer 311 is formed on an exposed surface of the dielectric layer 314 and sidewalls of the partition wall 315.
Thereafter, the electrically insulating substrate 301 is caused to overlap the electrically insulating substrate 302 such that the protection layer 313 formed on the electrically insulating substrate 302 makes contact with the partition wall 315 formed on the electrically insulating substrate 301, and that the data electrodes 307 extend perpendicularly to the scanning and common electrodes 305 and 304.
Then, thermal treatment is applied to the electrically insulating substrates 301 and 302 overlapping each other to thereby adhere them to each other at their ends by virtue of flits. Thus, a space defined by the electrically insulating substrates 301 and 302 and a seal layer (not illustrated) comprised of the flits is hermetically sealed.
Thereafter, the space is evacuated of air, and then, filled with discharge gas.
Thus, there is completed the plasma display panel 300 illustrated in FIG. 1.
When the plasma display panel 300 is fabricated as a color plasma display panel, RGB phosphor layers which emit red (R), green (G) and blue (B) lights are arranged in every three display cells. Specifically, a phosphor layer composed of phosphor which emits a red light, a phosphor layer composed of phosphor which emits a green light, and a phosphor layer composed of phosphor which emits a blue light are vertically and horizontally arranged in this order.
Among those three phosphor layers, a phosphor layer which emits a blue light is accompanied with a problem that an initial brightness and a lifetime collide with each other, and this problem remains unsolved. Specifically, if a phosphor layer emitting a blue light is composed of a material providing a desired initial brightness, the phosphor layer could not have a sufficient lifetime, and in contrast, if a phosphor layer emitting a blue light is composed of a material providing a desired lifetime, the phosphor layer could not have a sufficient initial brightness.
Hence, many attempts have been made to solve the above-mentioned problem in a phosphor layer emitting a blue light.
For instance, Japanese Patent Application Publication No. 2002-332481(A) has suggested phosphor composed of silicate and being excited by ultra-violet rays in vacuum condition, as a material of which a phosphor layer emitting a blue light is composed.
Specifically, the Publication suggests the phosphor composed of mM1O.nM2O.2M3O2 containing at least one of Eu and Mn as an additive, wherein M1 indicates at least one of Ca, Sr and Ba, M2 indicates at least one of Mg and Zn, M3 indicates at least one of Si and Ge, m is equal to or greater than 0.5, but equal to or smaller than 3.5 (0.5≦m≦3.5), n is equal to or greater than 0.5, but equal to or smaller than 2.5 (0.5≦m≦2.5), and M1 indicates at least two of Ca, Sr and Ba, or Sr, or Ba when m and n are equal to one (m=n=1).
Japanese Patent Application Publication No. 2001-84911(A) has suggested a plasma display panel including a phosphor layer composed of a mixture of phosphors emitting different-colored lights.
Specifically, at least one of a phosphor layer emitting a red light, a phosphor layer emitting a green light, and a phosphor layer emitting a blue light is composed of a mixture of phosphor emitting a red, green or blue light and phosphor emitting a different-colored light.
The phosphor suggested in the firstly mentioned Publication has an advantage that variation in a brightness with the lapse of time is small, but is accompanied with a problem that an initial brightness is low.
The firstly mentioned Publication has an object of suppressing variation in a brightness wit the lapse of time, caused by thermal treatment or exposure to plasma. The object can be performed by selecting phosphor composed of silicate and excited by ultra-violet rays in vacuum condition, as a material of which a phosphor layer emitting a blue light is composed. However, the suggested phosphor is accompanied with a problem that it can suppress variation in a brightness wit the lapse of time, but it unavoidably sacrifices an initial brightness.
The secondly mentioned Publication has an object of controlling a color coordinate (color temperature) when a white light is to be emitted, that is, when red, green and blue lights are emitted. This object can be performed by composing a phosphor layer of a mixture of first phosphor emitting a certain color light, and second phosphor emitting another color light. However, the suggested plasma display panel is accompanied with a problem that a color degree is unavoidably reduced when a blue light is singly emitted.